Cooled conductive balloon RF catheter for renal nerve ablation

ABSTRACT

A catheter includes a flexible shaft having a lumen arrangement and a length sufficient to access a target vessel of a patient. A balloon at the distal end of the shaft is fluidly coupled to the lumen arrangement. The balloon body comprises a first material and a second material different from the first material. The second material comprises a hydrophilic polymer that becomes electrically conductive in response to absorption of the conductive fluid. The fluid conductive regions facilitate perfusion of the conductive fluid through the balloon body to an inner wall of the target vessel during ablation of perivascular tissues. A cooling arrangement is configured for one of receiving a thermal transfer fluid from the lumen arrangement or facilitating perfusion of blood passing through the target vessel to cool the balloon body during ablation of the perivascular tissues.

RELATED APPLICATIONS

This application claims the benefit of Provisional Patent Application Ser. Nos. 61/411,795 filed Nov. 9, 2010 and 61/369,442 filed Jul. 30, 2010, to which priority is claimed pursuant to 35 U.S.C. §119(e) and which are hereby incorporated herein by reference in their entirety.

SUMMARY

Embodiments of the disclosure are generally directed to apparatuses and methods for ablating target tissue of the body from within a vessel using electrical energy. Embodiments are directed to cooled radiofrequency (RF) ablation catheters, systems, and methods. Various embodiments of the disclosure are directed to apparatuses and methods for ablating perivascular renal nerves using electrical energy, such as RF electrical energy.

Apparatuses, according to some embodiments, include a catheter comprising a flexible shaft having a proximal end, a distal end, a length, and a lumen arrangement extending between the proximal and distal ends. The shaft is preferably sufficient in length to access a target vessel of a patient relative to a percutaneous location. A balloon is provided at the distal end of the shaft and fluidly coupled to the lumen arrangement. The distal end of the shaft and the balloon are dimensioned for deployment within the target vessel.

The balloon includes a balloon body comprising a first material and an inlet manifold coupled to the lumen arrangement through which an electrically conductive fluid can pass into the balloon body. One or more fluid conductive regions are provided on the balloon body and comprise a second material different from the first material. The second material preferably comprises a hydrophilic polymer that becomes electrically conductive in response to absorption of the conductive fluid. The fluid conductive regions facilitate perfusion of the conductive fluid through the balloon body to an inner wall of the target vessel.

One or more electrical conductors extend at least partially along the catheter shaft and terminate proximate or within the balloon body. The one or more electrical conductors are configured to conduct electrical energy received from an external energy source to the one or more fluid conductive regions sufficient to ablate perivascular tissues proximate the balloon body. A cooling arrangement is configured for at least one of receiving a thermal transfer fluid from the lumen arrangement and facilitating perfusion of blood passing through the target vessel to cool the balloon body during ablation of the perivascular tissues.

Apparatuses, according to some embodiments, include a catheter comprising a flexible shaft having a proximal end, a distal end, a length, and a lumen arrangement extending between the proximal and distal ends. The shaft preferably has a length sufficient to access a target vessel of a patient relative to a percutaneous access location. A balloon is provided at the distal end of the shaft and fluidly coupled to the lumen arrangement. The distal end of the shaft and the balloon are dimensioned for deployment within the target vessel.

The balloon includes a balloon body formed of a hydrophilic polymer that becomes electrically conductive in response to absorption of a conductive fluid. The balloon body comprises a proximal conical section, a distal conical section, and a circumferential section defined between the proximal and distal conical sections. The circumferential section is configured to contact a circumferential portion of an inner wall of the target vessel. The circumferential section has a thickness less than that of the proximal and distal conical sections sufficient to facilitate preferential perfusion of the conductive fluid through the circumferential section relative to the proximal and distal conical sections.

An inlet manifold is coupled to the lumen arrangement through which the electrically conductive fluid can pass into the balloon body. An electrical conductor extends at least partially along the shaft and terminates proximate or within the balloon body. The electrical conductor is coupled to an electrode positioned within the balloon body and configured to conduct electrical energy received from an external energy source to at least the circumferential section of the balloon body sufficient to ablate perivascular tissues proximate the circumferential section. A cooling arrangement is configured for at least one of receiving a thermal transfer fluid from the lumen arrangement and facilitating perfusion of blood passing through the target vessel to cool the balloon body during ablation of the perivascular tissues.

In various embodiments, the target vessel comprises an artery of the patient. In some embodiments, the target vessel comprises a renal artery of the patient, and the perivascular tissues comprise renal nerves. According to various embodiments, the electrical energy comprises radiofrequency electrical energy.

These and other features can be understood in view of the following detailed discussion and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of a right kidney and renal vasculature including a renal artery branching laterally from the abdominal aorta;

FIGS. 2A and 2B illustrate sympathetic innervation of the renal artery;

FIG. 3A illustrates various tissue layers of the wall of the renal artery;

FIGS. 3B and 3C illustrate a portion of a renal nerve;

FIG. 4A is a cross section of a balloon catheter comprising a multiplicity of fluid conductive regions formed of a hydrophilic polymer deployed at a treatment location of the body in accordance with various embodiments;

FIG. 4B is a cross section of a balloon body comprising a fluid conductive region formed of a hydrophilic polymer in accordance with various embodiments;

FIG. 5A illustrates a balloon catheter comprising a multiplicity of fluid conductive regions formed of a hydrophilic polymer and a cooling arrangement in accordance with various embodiments

FIG. 5B is a cross section of a shaft of the balloon catheter shown in FIG. 5A in accordance with various embodiments;

FIG. 6 illustrates a balloon catheter comprising one or more fluid conductive regions formed of a hydrophilic polymer and a cooling arrangement in accordance with various embodiments;

FIG. 7 illustrates a balloon catheter comprising one or more fluid conductive regions formed of a hydrophilic polymer and a cooling arrangement in accordance with various embodiments;

FIG. 8A illustrates a balloon catheter comprising one or more fluid conductive regions formed of a hydrophilic polymer and a cooling arrangement in accordance with various embodiments;

FIG. 8B illustrates a portion of the balloon body shown in FIG. 8A, which shows a metalized layer that serves as an electrically conductive pad situated at least partially around the fluid conductive regions in accordance with various embodiments;

FIG. 9A-9D show several illustrations of balloons that incorporate one or more fluid conductive regions that serve as RF electrodes in response to absorption of an electrolytic fluid in accordance with various embodiments;

FIG. 10 illustrates a catheter which includes a conductive hydrophilic material in the construction of the balloon body in accordance with various embodiments;

FIG. 11 shows a portion of the balloon wall depicted in FIG. 10 which defines an RF electrode region in accordance with various embodiments;

FIG. 12 shows an electrode configuration at the circumferential section of the balloon shown in FIG. 11 in accordance with various embodiments; and

FIG. 13 shows an electrode configuration at the circumferential section of the balloon shown in FIG. 11 in accordance with various embodiments.

DESCRIPTION

Embodiments of the disclosure are directed to apparatuses and methods for ablating perivascular renal nerves for the treatment of hypertension. Embodiments of the disclosure are directed to an improved cooled RF ablation catheter and system.

RF ablation catheters for ablation of cardiac arrhythmias are known, but are not readily adaptable or optimized for ablation of perivascular renal nerves. Apparatuses of the disclosure can be configured to place one or more electrodes in a predictable pattern and provide cooling to protect the renal artery. In some embodiments, a catheter arrangement is configured to incorporate multiple electrodes spaced circumferentially and axially which can be used to ablate the perivascular renal nerves while minimizing renal artery injury. In other embodiments, a catheter arrangement is configured to incorporate one or more electrodes arranged in an annular or circumferential band shape which can be used to ablate the perivascular renal nerves while minimizing renal artery injury. A cooling media can be delivered to the catheter arrangement or a blood perfusion lumen can be used to provide cooling for the wall of the renal artery.

Embodiments disclosed herein are particularly well suited for use in the treatment of hypertension. Hypertension is a chronic medical condition in which the blood pressure is elevated. Persistent hypertension is a significant risk factor associated with a variety of adverse medical conditions, including heart attacks, heart failure, arterial aneurysms, and strokes. Persistent hypertension is a leading cause of chronic renal failure. Hyperactivity of the sympathetic nervous system serving the kidneys is associated with hypertension and its progression. Deactivation of nerves in the kidneys via renal denervation can reduce blood pressure, and may be a viable treatment option for many patients with hypertension who do not respond to conventional drugs.

The kidneys are instrumental in a number of body processes, including blood filtration, regulation of fluid balance, blood pressure control, electrolyte balance, and hormone production. One primary function of the kidneys is to remove toxins, mineral salts, and water from the blood to form urine. The kidneys receive about 20-25% of cardiac output through the renal arteries that branch left and right from the abdominal aorta, entering each kidney at the concave surface of the kidneys, the renal hilum.

Blood flows into the kidneys through the renal artery and the afferent arteriole, entering the filtration portion of the kidney, the renal corpuscle. The renal corpuscle is composed of the glomerulus, a thicket of capillaries, surrounded by a fluid-filled, cup-like sac called Bowman's capsule. Solutes in the blood are filtered through the very thin capillary walls of the glomerulus due to the pressure gradient that exists between the blood in the capillaries and the fluid in the Bowman's capsule. The pressure gradient is controlled by the contraction or dilation of the arterioles. After filtration occurs, the filtered blood moves through the efferent arteriole and the peritubular capillaries, converging in the interlobular veins, and finally exiting the kidney through the renal vein.

Particles and fluid filtered from the blood move from the Bowman's capsule through a number of tubules to a collecting duct. Urine is formed in the collecting duct and then exits through the ureter and bladder. The tubules are surrounded by the peritubular capillaries (containing the filtered blood). As the filtrate moves through the tubules and toward the collecting duct, nutrients, water, and electrolytes, such as sodium and chloride, are reabsorbed into the blood.

The kidneys are innervated by the renal plexus which emanates primarily from the aorticorenal ganglion. Renal ganglia are formed by the nerves of the renal plexus as the nerves follow along the course of the renal artery and into the kidney. The renal nerves are part of the autonomic nervous system which includes sympathetic and parasympathetic components. The sympathetic nervous system is known to be the system that provides the bodies “fight or flight” response, whereas the parasympathetic nervous system provides the “rest and digest” response. Stimulation of sympathetic nerve activity triggers the sympathetic response which causes the kidneys to increase production of hormones that increase vasoconstriction and fluid retention. This process is referred to as the renin-angiotensin-aldosterone-system (RAAS) response to increased renal sympathetic nerve activity.

In response to a reduction in blood volume, the kidneys secrete renin, which stimulates the production of angiotensin. Angiotensin causes blood vessels to constrict, resulting in increased blood pressure, and also stimulates the secretion of the hormone aldosterone from the adrenal cortex. Aldosterone causes the tubules of the kidneys to increase the reabsorption of sodium and water, which increases the volume of fluid in the body and blood pressure.

Congestive heart failure (CHF) is a condition that has been linked to kidney function. CHF occurs when the heart is unable to pump blood effectively throughout the body. When blood flow drops, renal function degrades because of insufficient perfusion of the blood within the renal corpuscles. The decreased blood flow to the kidneys triggers an increase in sympathetic nervous system activity (i.e., the RAAS becomes too active) that causes the kidneys to secrete hormones that increase fluid retention and vasorestriction. Fluid retention and vasorestriction in turn increases the peripheral resistance of the circulatory system, placing an even greater load on the heart, which diminishes blood flow further. If the deterioration in cardiac and renal functioning continues, eventually the body becomes overwhelmed, and an episode of heart failure decompensation occurs, often leading to hospitalization of the patient.

FIG. 1 is an illustration of a right kidney 10 and renal vasculature including a renal artery 12 branching laterally from the abdominal aorta 20. In FIG. 1, only the right kidney 10 is shown for purposes of simplicity of explanation, but reference will be made herein to both right and left kidneys and associated renal vasculature and nervous system structures, all of which are contemplated within the context of embodiments of the disclosure. The renal artery 12 is purposefully shown to be disproportionately larger than the right kidney 10 and abdominal aorta 20 in order to facilitate discussion of various features and embodiments of the present disclosure.

The right and left kidneys are supplied with blood from the right and left renal arteries that branch from respective right and left lateral surfaces of the abdominal aorta 20. Each of the right and left renal arteries is directed across the crus of the diaphragm, so as to form nearly a right angle with the abdominal aorta 20. The right and left renal arteries extend generally from the abdominal aorta 20 to respective renal sinuses proximate the hilum 17 of the kidneys, and branch into segmental arteries and then interlobular arteries within the kidney 10. The interlobular arteries radiate outward, penetrating the renal capsule and extending through the renal columns between the renal pyramids. Typically, the kidneys receive about 20% of total cardiac output which, for normal persons, represents about 1200 mL of blood flow through the kidneys per minute.

The primary function of the kidneys is to maintain water and electrolyte balance for the body by controlling the production and concentration of urine. In producing urine, the kidneys excrete wastes such as urea and ammonium. The kidneys also control reabsorption of glucose and amino acids, and are important in the production of hormones including vitamin D, renin and erythropoietin.

An important secondary function of the kidneys is to control metabolic homeostasis of the body. Controlling hemostatic functions include regulating electrolytes, acid-base balance, and blood pressure. For example, the kidneys are responsible for regulating blood volume and pressure by adjusting volume of water lost in the urine and releasing erythropoietin and renin, for example. The kidneys also regulate plasma ion concentrations (e.g., sodium, potassium, chloride ions, and calcium ion levels) by controlling the quantities lost in the urine and the synthesis of calcitrol. Other hemostatic functions controlled by the kidneys include stabilizing blood pH by controlling loss of hydrogen and bicarbonate ions in the urine, conserving valuable nutrients by preventing their excretion, and assisting the liver with detoxification.

Also shown in FIG. 1 is the right suprarenal gland 11, commonly referred to as the right adrenal gland. The suprarenal gland 11 is a star-shaped endocrine gland that rests on top of the kidney 10. The primary function of the suprarenal glands (left and right) is to regulate the stress response of the body through the synthesis of corticosteroids and catecholamines, including cortisol and adrenaline (epinephrine), respectively. Encompassing the kidneys 10, suprarenal glands 11, renal vessels 12, and adjacent perirenal fat is the renal fascia, e.g., Gerota's fascia, (not shown), which is a fascial pouch derived from extraperitoneal connective tissue.

The autonomic nervous system of the body controls involuntary actions of the smooth muscles in blood vessels, the digestive system, heart, and glands. The autonomic nervous system is divided into the sympathetic nervous system and the parasympathetic nervous system. In general terms, the parasympathetic nervous system prepares the body for rest by lowering heart rate, lowering blood pressure, and stimulating digestion. The sympathetic nervous system effectuates the body's fight-or-flight response by increasing heart rate, increasing blood pressure, and increasing metabolism.

In the autonomic nervous system, fibers originating from the central nervous system and extending to the various ganglia are referred to as preganglionic fibers, while those extending from the ganglia to the effector organ are referred to as postganglionic fibers. Activation of the sympathetic nervous system is effected through the release of adrenaline (epinephrine) and to a lesser extent norepinephrine from the suprarenal glands 11. This release of adrenaline is triggered by the neurotransmitter acetylcholine released from preganglionic sympathetic nerves.

The kidneys and ureters (not shown) are innervated by the renal nerves 14. FIGS. 1 and 2A-2B illustrate sympathetic innervation of the renal vasculature, primarily innervation of the renal artery 12. The primary functions of sympathetic innervation of the renal vasculature include regulation of renal blood flow and pressure, stimulation of renin release, and direct stimulation of water and sodium ion reabsorption.

Most of the nerves innervating the renal vasculature are sympathetic postganglionic fibers arising from the superior mesenteric ganglion 26. The renal nerves 14 extend generally axially along the renal arteries 12, enter the kidneys 10 at the hilum 17, follow the branches of the renal arteries 12 within the kidney 10, and extend to individual nephrons. Other renal ganglia, such as the renal ganglia 24, superior mesenteric ganglion 26, the left and right aorticorenal ganglia 22, and celiac ganglia 28 also innervate the renal vasculature. The celiac ganglion 28 is joined by the greater thoracic splanchnic nerve (greater TSN). The aorticorenal ganglia 26 is joined by the lesser thoracic splanchnic nerve (lesser TSN) and innervates the greater part of the renal plexus.

Sympathetic signals to the kidney 10 are communicated via innervated renal vasculature that originates primarily at spinal segments T10-T12 and L1. Parasympathetic signals originate primarily at spinal segments S2-S4 and from the medulla oblongata of the lower brain. Sympathetic nerve traffic travels through the sympathetic trunk ganglia, where some may synapse, while others synapse at the aorticorenal ganglion 22 (via the lesser thoracic splanchnic nerve, i.e., lesser TSN) and the renal ganglion 24 (via the least thoracic splanchnic nerve, i.e., least TSN). The postsynaptic sympathetic signals then travel along nerves 14 of the renal artery 12 to the kidney 10. Presynaptic parasympathetic signals travel to sites near the kidney 10 before they synapse on or near the kidney 10.

With particular reference to FIG. 2A, the renal artery 12, as with most arteries and arterioles, is lined with smooth muscle 34 that controls the diameter of the renal artery lumen 13. Smooth muscle, in general, is an involuntary non-striated muscle found within the media layer of large and small arteries and veins, as well as various organs. The glomeruli of the kidneys, for example, contain a smooth muscle-like cell called the mesangial cell. Smooth muscle is fundamentally different from skeletal muscle and cardiac muscle in terms of structure, function, excitation-contraction coupling, and mechanism of contraction.

Smooth muscle cells can be stimulated to contract or relax by the autonomic nervous system, but can also react on stimuli from neighboring cells and in response to hormones and blood borne electrolytes and agents (e.g., vasodilators or vasoconstrictors). Specialized smooth muscle cells within the afferent arteriole of the juxtaglomerular apparatus of kidney 10, for example, produces renin which activates the angiotension II system.

The renal nerves 14 innervate the smooth muscle 34 of the renal artery wall 15 and extend lengthwise in a generally axial or longitudinal manner along the renal artery wall 15. The smooth muscle 34 surrounds the renal artery circumferentially, and extends lengthwise in a direction generally transverse to the longitudinal orientation of the renal nerves 14, as is depicted in FIG. 2B.

The smooth muscle 34 of the renal artery 12 is under involuntary control of the autonomic nervous system. An increase in sympathetic activity, for example, tends to contract the smooth muscle 34, which reduces the diameter of the renal artery lumen 13 and decreases blood perfusion. A decrease in sympathetic activity tends to cause the smooth muscle 34 to relax, resulting in vessel dilation and an increase in the renal artery lumen diameter and blood perfusion. Conversely, increased parasympathetic activity tends to relax the smooth muscle 34, while decreased parasympathetic activity tends to cause smooth muscle contraction.

FIG. 3A shows a segment of a longitudinal cross-section through a renal artery, and illustrates various tissue layers of the wall 15 of the renal artery 12. The innermost layer of the renal artery 12 is the endothelium 30, which is the innermost layer of the intima 32 and is supported by an internal elastic membrane. The endothelium 30 is a single layer of cells that contacts the blood flowing though the vessel lumen 13. Endothelium cells are typically polygonal, oval, or fusiform, and have very distinct round or oval nuclei. Cells of the endothelium 30 are involved in several vascular functions, including control of blood pressure by way of vasoconstriction and vasodilation, blood clotting, and acting as a barrier layer between contents within the lumen 13 and surrounding tissue, such as the membrane of the intima 32 separating the intima 32 from the media 34, and the adventitia 36. The membrane or maceration of the intima 32 is a fine, transparent, colorless structure which is highly elastic, and commonly has a longitudinal corrugated pattern.

Adjacent the intima 32 is the media 33, which is the middle layer of the renal artery 12. The media is made up of smooth muscle 34 and elastic tissue. The media 33 can be readily identified by its color and by the transverse arrangement of its fibers. More particularly, the media 33 consists principally of bundles of smooth muscle fibers 34 arranged in a thin plate-like manner or lamellae and disposed circularly around the arterial wall 15. The outermost layer of the renal artery wall 15 is the adventitia 36, which is made up of connective tissue. The adventitia 36 includes fibroblast cells 38 that play an important role in wound healing.

A perivascular region 37 is shown adjacent and peripheral to the adventitia 36 of the renal artery wall 15. A renal nerve 14 is shown proximate the adventitia 36 and passing through a portion of the perivascular region 37. The renal nerve 14 is shown extending substantially longitudinally along the outer wall 15 of the renal artery 12. The main trunk of the renal nerves 14 generally lies in or on the adventitia 36 of the renal artery 12, often passing through the perivascular region 37, with certain branches coursing into the media 33 to enervate the renal artery smooth muscle 34.

Embodiments of the disclosure may be implemented to provide varying degrees of denervation therapy to innervated renal vasculature. For example, embodiments of the disclosure may provide for control of the extent and relative permanency of renal nerve impulse transmission interruption achieved by denervation therapy delivered using a treatment apparatus of the disclosure. The extent and relative permanency of renal nerve injury may be tailored to achieve a desired reduction in sympathetic nerve activity (including a partial or complete block) and to achieve a desired degree of permanency (including temporary or irreversible injury).

Returning to FIGS. 3B and 3C, the portion of the renal nerve 14 shown in FIGS. 3B and 3C includes bundles 14 a of nerve fibers 14 b each comprising axons or dendrites that originate or terminate on cell bodies or neurons located in ganglia or on the spinal cord, or in the brain. Supporting tissue structures 14 c of the nerve 14 include the endoneurium (surrounding nerve axon fibers), perineurium (surrounds fiber groups to form a fascicle), and epineurium (binds fascicles into nerves), which serve to separate and support nerve fibers 14 b and bundles 14 a. In particular, the endoneurium, also referred to as the endoneurium tube or tubule, is a layer of delicate connective tissue that encloses the myelin sheath of a nerve fiber 14 b within a fasciculus.

Major components of a neuron include the soma, which is the central part of the neuron that includes the nucleus, cellular extensions called dendrites, and axons, which are cable-like projections that carry nerve signals. The axon terminal contains synapses, which are specialized structures where neurotransmitter chemicals are released in order to communicate with target tissues. The axons of many neurons of the peripheral nervous system are sheathed in myelin, which is formed by a type of glial cell known as Schwann cells. The myelinating Schwann cells are wrapped around the axon, leaving the axolemma relatively uncovered at regularly spaced nodes, called nodes of Ranvier. Myelination of axons enables an especially rapid mode of electrical impulse propagation called saltation.

In some embodiments, a treatment apparatus of the disclosure may be implemented to deliver denervation therapy that causes transient and reversible injury to renal nerve fibers 14 b. In other embodiments, a treatment apparatus of the disclosure may be implemented to deliver denervation therapy that causes more severe injury to renal nerve fibers 14 b, which may be reversible if the therapy is terminated in a timely manner. In preferred embodiments, a treatment apparatus of the disclosure may be implemented to deliver denervation therapy that causes severe and irreversible injury to renal nerve fibers 14 b, resulting in permanent cessation of renal sympathetic nerve activity. For example, a treatment apparatus may be implemented to deliver a denervation therapy that disrupts nerve fiber morphology to a degree sufficient to physically separate the endoneurium tube of the nerve fiber 14 b, which can prevent regeneration and re-innervation processes.

By way of example, and in accordance with Seddon's classification as is known in the art, a treatment apparatus of the disclosure may be implemented to deliver a denervation therapy that interrupts conduction of nerve impulses along the renal nerve fibers 14 b by imparting damage to the renal nerve fibers 14 b consistent with neruapraxia. Neurapraxia describes nerve damage in which there is no disruption of the nerve fiber 14 b or its sheath. In this case, there is an interruption in conduction of the nerve impulse down the nerve fiber, with recovery taking place within hours to months without true regeneration, as Wallerian degeneration does not occur. Wallerian degeneration refers to a process in which the part of the axon separated from the neuron's cell nucleus degenerates. This process is also known as anterograde degeneration. Neurapraxia is the mildest form of nerve injury that may be imparted to renal nerve fibers 14 b by use of a treatment apparatus according to embodiments of the disclosure.

A treatment apparatus may be implemented to interrupt conduction of nerve impulses along the renal nerve fibers 14 b by imparting damage to the renal nerve fibers consistent with axonotmesis. Axonotmesis involves loss of the relative continuity of the axon of a nerve fiber and its covering of myelin, but preservation of the connective tissue framework of the nerve fiber. In this case, the encapsulating support tissue 14 c of the nerve fiber 14 b are preserved. Because axonal continuity is lost, Wallerian degeneration occurs. Recovery from axonotmesis occurs only through regeneration of the axons, a process requiring time on the order of several weeks or months. Electrically, the nerve fiber 14 b shows rapid and complete degeneration. Regeneration and re-innervation may occur as long as the endoneural tubes are intact.

A treatment apparatus may be implemented to interrupt conduction of nerve impulses along the renal nerve fibers 14 b by imparting damage to the renal nerve fibers 14 b consistent with neurotmesis. Neurotmesis, according to Seddon's classification, is the most serious nerve injury in the scheme. In this type of injury, both the nerve fiber 14 b and the nerve sheath are disrupted. While partial recovery may occur, complete recovery is not possible. Neurotmesis involves loss of continuity of the axon and the encapsulating connective tissue 14 c, resulting in a complete loss of autonomic function, in the case of renal nerve fibers 14 b. If the nerve fiber 14 b has been completely divided, axonal regeneration causes a neuroma to form in the proximal stump.

A more stratified classification of neurotmesis nerve damage may be found by reference to the Sunderland System as is known in the art. The Sunderland System defines five degrees of nerve damage, the first two of which correspond closely with neurapraxia and axonotmesis of Seddon's classification. The latter three Sunderland System classifications describe different levels of neurotmesis nerve damage.

The first and second degrees of nerve injury in the Sunderland system are analogous to Seddon's neurapraxia and axonotmesis, respectively. Third degree nerve injury, according to the Sunderland System, involves disruption of the endoneurium, with the epineurium and perineurium remaining intact. Recovery may range from poor to complete depending on the degree of intrafascicular fibrosis. A fourth degree nerve injury involves interruption of all neural and supporting elements, with the epineurium remaining intact. The nerve is usually enlarged. Fifth degree nerve injury involves complete transection of the nerve fiber 14 b with loss of continuity.

Turning now to FIG. 4A, there is shown a cross section of a balloon catheter comprising a multiplicity of fluid conductive regions formed of a hydrophilic polymer deployed at a treatment location of the body in accordance with various embodiments. According to representative embodiments, the balloon catheter shown in FIG. 4A includes a balloon 102 dimensioned for deployment in a lumen 13 of a target vessel, such as a renal artery 12. The balloon 102 comprises a balloon body 103 that incorporates at least one, and preferably several, fluid conductive regions 120 formed of a hydrophilic polymer. The balloon 102 is preferably inflated using an electrically conductive fluid.

The fluid conductive regions 120 that define hydrophilic areas quickly absorb a water-based electrolytic solution (e.g., saline) to become conductive to RF electric current. Tecophilic™ or Tecogel™ polyurethanes or similar materials (e.g., thermoplastic polyurethanes) can be used to form the hydrophilic areas 120, for example, which absorb significant amounts of a water-based electrolyte and quickly become electrically conductive when wet. According to various embodiments, for example, the balloon body 103 includes a first material that comprises a non-conductive polymer material, and the one or more fluid conductive regions 120 provided on the balloon body 103 each comprise a conductive thermoplastic polyurethane.

The hydrophilic polymer at the fluid conductive regions 120 becomes electrically conductive in response to absorption of the conductive liquid used to pressurize the balloon 102. Preferably, the balloon 102 is pressurized to a pressure (P1) greater than a pressure (P2) surrounding the balloon 102. The pressure (P2) surrounding the balloon 102 may be the pressure of blood passing within the renal artery 12, for example. By way of further example, the pressure (P2) surrounding the balloon 102 may be the pressure of tissue at a treatment location of the body that exerts a force against the body 103 of the balloon 102.

A pressure differential developed by pressurizing the balloon 102 to a pressure greater than that surrounding the balloon 102 facilitates perfusion of the conductive liquid through the fluid conductive regions 120 of the balloon body 103 and into a gap 19 (exaggerated in FIG. 4A) between an exterior surface of the balloon body 13 and the inner wall of the renal artery 12. In this scenario, when the fluid conductive regions 120 are energized using an RF power source, RF energy is conducted through the wall of the balloon body 103 and to the artery wall via the fluid conductive regions 120 and conductive fluid perfusion through the conducive regions 120. The RF energy conducted to the artery wall is preferably sufficient to ablate renal nerves 14 included in the perivascular space adjacent the renal artery 12 or those located on or within the adventitia of the renal artery 12. The RF energy conducted to the artery wall can be selected to ablate both renal nerves 14 and ganglia of the renal artery 12 (e.g., ganglia on the renal artery or ganglia included within the perivascular space adjacent the renal artery 12).

In some embodiments, the RF energy can be conducted to the fluid conductive regions 120 via the fluid used to pressurize the balloon 102. In other embodiments, the RF energy can be conducted to the fluid conductive regions 120 via one or more electrical conductors situated within the wall of the balloon body 103 or along an interior or exterior surface of the balloon body 103.

For example, one or more electrical conductors can extend at least partially into the balloon 102 and be positioned in a spaced-apart relationship with respect to the one or more fluid conductive regions 120. In other configurations, one or more electrical conductors can extend along at least a portion of the balloon body 103 and electrically connect to the one or more fluid conductive regions 120. As shown in FIG. 4B, for example, one or more electrical conductors 110 b can be situated within the wall of the balloon body 103, and electrically connect with one or more fluid conductive regions 120 via metallization layers 111 b, 111 a. Alternatively or in addition, one or more electrical conductors 110 a can be situated along an interior wall 115 (or an exterior wall) of the balloon body 103, and electrically connect with one or more fluid conductive regions 120 via metallization layer(s) 111 a.

Perfusion of the conductive liquid through the fluid conductive regions 120 and into the gap 19 between the exterior surface of the balloon body 13 and the inner wall of the renal artery 12 serves to increase the effective size of the RF electrodes defined by the fluid conductive regions 120, resulting in formation of larger lesions and enhanced distribution of current densities at the electrode-tissue interface. In particular, the electrically conductive fluid that permeates through fluid conductive regions 120 will intimately and totally contact adjacent tissue, and even penetrate into tissue, providing a path for RF current to penetrate into the tissues. By contrast, a metal electrode on the balloon surface may or may not be in good contact with tissue, depending upon the details of the geometry of the artery wall at the electrode location. Metal electrode contact could be improved by increasing the height of electrode bumps on the balloon surface, however this approach could mechanically traumatize the artery wall.

Prior art RF ablation catheters typically contain a plurality of conductors that terminate in platinum iridium electrodes. Placement of relatively heavy electrodes on a very thin balloon wall may be difficult and awkward. By contrast, fluid conductive electrodes 120 of the present invention are contained within the balloon wall, and add no weight or electrode protrusion from the balloon wall.

According to some embodiments, a multiplicity of fluid conductive regions 120 are energized by a single electrode that resides within balloon 102. In these embodiments, RF energy is conducted from the single electrode to the fluid conductive regions 120 through the conductive balloon inflation fluid. Energizing multiple regions 120 from a single electrode provides a catheter with increased flexibility and reduced profile compared to the alternative of energizing each electrode from a separate conductor. Conventional metallic electrodes are typically not energized by a single conductor, because current would flow through the electrode adjacent tissue having the path of least resistance to the patient ground pad. Electrodes adjacent higher resistance tissue would receive insufficient current for ablation. By contrast, fluid conductive regions 120 may have electrical resistance that is larger than the tissue resistance. Since all fluid conductive regions 120 are identical, they will have approximately the same resistance to current flow and provide relatively uniform ablations at each electrode. While heat is generated in the fluid conductive regions 120 due to their electrical resistance, this heat is dissipated by the cooling fluid.

According to some embodiments, and with reference to FIG. 5A, a renal denervation apparatus includes a catheter 100 comprising a flexible shaft 104 having a proximal end, a distal end, a length, and a lumen arrangement 105 extending between the proximal and distal ends. The length of the shaft 104 is sufficient to access a treatment location of the body, such as a patient's renal artery, relative to a percutaneous location. A balloon 102 is provided at the distal end of the shaft 104 and is fluidly coupled to the lumen arrangement 105. The distal end of the shaft 104 and the balloon 102 are dimensioned for deployment within the treatment location of the body (e.g., the renal artery).

In some embodiments, the balloon 102 includes a balloon body 103 comprising a first material. A manifold 107 is fluidly coupled to the lumen arrangement 105 through which an electrically conductive liquid can pass into the balloon body 103. One or more fluid conductive regions 120 are provided on the balloon body 103 and comprise a second material different from the first material. The second material preferably comprises a hydrophilic polymer that becomes electrically conductive in response to absorption of the conductive liquid. The one or more fluid conductive regions 120 facilitate perfusion of the conductive liquid through the one or more fluid conductive regions 120 to an inner wall of the treatment location of the body, such as the renal artery.

One or more electrical conductors defining a conductor arrangement 110 extend at least partially along the shaft 104 and terminate proximate or within the balloon body 103. The one or more electrical conductors 110 are configured to conduct RF energy received from an external energy source (not shown) to the one or more fluid conductive regions 120 sufficient to ablate target tissue at the treatment location of the body, such as perivascular renal nerves adjacent to and/or innervating the renal artery. Current returns to the RF energy source through a patient ground pad (not shown).

FIG. 5B shows a cross section of the shaft 104 of the balloon catheter of FIG. 5A, which includes a conductor lumen 113, a guide wire lumen 111, a supply lumen 106, and a return lumen 108. The supply and return lumens 106, 108 deliver a cooling fluid to the balloon 102 and remove spent cooling fluid from the balloon 102, respectively. The supply and return lumens 106, 108 are respectively coupled to supply and return connectors of an external coolant source situated at the proximal end of the catheter 100. In some embodiments, conductive fluid is supplied by lumen 106, and exits the distal end of the balloon 102 through a lumen adjacent to or surrounding guidewire lumen 111 in FIG. 5A. In this embodiment, return lumen 108 is not required. The conductive fluid both inflates the balloon 102 and provides continuous cooling. The conductive cooling/inflation fluid in this embodiment is compatible with blood, for example a saline solution.

The conductor lumen 113 may include a layer of electrically insulating material and/or the one or more conductors disposed in the conductor lumen 113 may each include an insulating layer. The guide wire lumen 111 is dimensioned to receive a guide wire or other elongated navigation assist member that can by used by the clinician to facilitate delivery of the balloon 102 into the renal artery.

In the configuration shown in FIG. 5A, the guide wire lumen 111 defines an open lumen of the balloon 102, which allows for advancement of a guide wire 112 therethrough for navigating the balloon 102 to the renal artery. After the guide wire 112 is positioned within the renal artery, the balloon catheter 100 is advanced along the guide wire 112 and delivered to the lumen of the renal artery using an over-the-wire or rail delivery technique.

In some embodiments, a cooling arrangement is configured to receive a thermal transfer fluid from the lumen arrangement 105. Preferably, the thermal transfer fluid is an electrically conductive fluid used to pressurize the balloon 102, such as cooled saline. In other embodiments, the cooling arrangement includes a cooling fluid lumen configured to facilitate perfusion of blood passing through the renal artery to cool the balloon body 103 during ablation of the perivascular renal nerves.

FIG. 6 shows an embodiment of a catheter 100 which includes a cooling lumen arrangement 130 configured to shunt blood passing through the renal artery to cool the balloon body 103 during ablation. A balloon 102 of the catheter 100 is shown deployed within a renal artery 12, with blood depicted as flowing from right to left across the page. The balloon 102 incorporates one or more cooling lumens 130 that receive blood passing through the renal artery 12 at an inlet 132. The blood passes through cooling lumens 130 and serves as a thermal transfer fluid that reduces the temperature of the electrode-tissue interface. Blood passing through the cooling lumens 130 exits the balloon 120 at an output 134. The number and diameter of the cooling lumens 130 can be selected based on the expected amount of heat to be removed at the electrode-tissue interface during renal nerve ablation.

It is noted that other cooling arrangements that use blood as a thermal transfer agent are contemplated, such as inlet and outlet ports provided on the shaft 104 that are fluidly coupled to cooling lumens 130 or to a cooling bladder/balloon that is encompassed by the balloon 102. In some embodiments, the cooling arrangement may constitute longitudinal or spiral channels or flutes built into the balloon body 103. Blood passing through channels or flutes serves to cool the wall of the renal artery 12 during ablation.

FIG. 7 shows a balloon 102 that incorporates a cooling arrangement in accordance with various embodiments. The balloon 102 shown in FIG. 7 incorporates a supply lumen 106 and a return lumen 108 that respectively extend along the shaft 104 between the balloon 102 and a proximal end of the shaft 104. The supply lumen 106 is fluidly coupled to one or more inlet ports 136 through which a thermal transfer fluid passes and enters the balloon 102. The return lumen 106 is fluidly coupled to one or more outlet ports 138 through which spent thermal transfer fluid passes and exits the balloon 102.

The supply and return lumens 106, 108 are respectively coupled to supply and return couplings of an external coolant source. The volumetric flow rate of thermal transfer fluid through the balloon 102 is regulated by the external coolant source. For example, the amount of pressurization of the balloon 102 and the rate of thermal transfer fluid through the balloon 102 can be regulated by appropriately controlling the pressure and/or flow rate of the fluid respectively delivered to the supply lumen 106 and removed from the return lumen 108 at the external coolant source.

In some embodiments, the thermal transfer fluid is an electrically conductive fluid, such as saline, which is used for balloon pressurization, cooling of the electrode-tissue interface, and current conduction between one or more electrical conductors 110 extending into the balloon 102 from the shaft 104 and the one or more fluid conductive regions 120. In other embodiments in which the one or more electrical conductors 110 a, 110 b are connected to respective fluid conductive regions 120, as is shown in FIG. 7, the thermal transfer fluid need not be electrically conductive. It is noted that in the representative embodiment shown in FIG. 7, the electrical conductors extend from the shaft 104 and through a wall of the balloon body 103. In some embodiments, one or more electrical conductors can extend from the shaft 104 and through one or more conductor lumens disposed on or adjacent either the interior wall or exterior wall of the balloon body 103.

FIG. 8A shows a catheter 100 that includes a balloon 102 having one or more fluid conductive regions 120 that serve as RF electrodes in response to absorption of an electrolytic fluid in accordance with various embodiments. In the embodiment shown in FIG. 8A, discrete patches of conductive material 120 can be energized separately, with various voltage waveforms and durations and timing chosen to ablate separate tissue regions in a desired temporal and spatial pattern. An external control unit and patient ground pad electrode (not shown) facilitates RF energy delivery to the fluid conductive regions 120 in the chosen pattern.

FIGS. 8A and 8B illustrate a balloon configuration which includes a metalized layer that serves as an electrically conductive pad 109 situated at least partially around the fluid conductive regions 120 for enhanced energy transfer. The metalized layers preferably connect to separate conductors 110 as needed to achieve the desired pattern by metalized paths or conductors incorporated into the balloon 102.

The balloon 102 of FIGS. 8A and 8B can be similar to those embodiments previously described with reference to FIGS. 5A and 5B, with the addition of an electrically conductive pad 109 associated with each of the fluid conductive regions 120. For example, and as best seen in FIG. 8A, the balloon body 103 includes one or more electrically conductive pads 109 each of which is at least partially encompasses the one or more fluid conductive regions 120. One or more electrical conductors 110 extend along at least a portion of the balloon body 103 and are connected to respective electrically conductive pads 109. Electrical conductors 110 may consists of insulated fine wire. Alternatively, conductors 110 may be printed onto the surface of balloon 102 using conductive ink. Printed lines may then be electrically insulated with a thin film coating. Conductors 110 may then continue down catheter body 104 as insulated wires within the catheter or within the wall of the catheter, or as insulated conductive lines printed on the catheter body.

In various embodiments where individual fluid conductive regions 120 (with or without electrically conductive pads 109) are electrically coupled to individual conductors 110, the individual fluid conductive regions and/or electrically conductive pads can be separately energized to achieve voltage waveforms and durations and timing selected to ablate separate tissue regions in a desired temporal and spatial pattern, as discussed previously.

FIG. 9A-9D show several illustrations of balloons 102 that incorporate one or more fluid conductive regions 120 that serve as RF electrodes in response to absorption of an electrolytic fluid in accordance with various embodiments. In general, one or more circumferential, axial, or helical stripes of conductive material 120 can be used, or discrete patches of conductive material 120 that provide discrete areas of conductivity can be used. For example, a helical stripe electrode or a helical series of separate spot electrodes can be fabricated using a conductive polymer according to some configurations. In other configurations, circumferential or axial stripes or patterns can be used.

Discrete conductive areas 120 can be fabricated using multiple layers and masking, for example. RF energy is carried by one or more metal conductors of a conductor arrangement 110 from a connected external control unit (not shown) along the catheter 104 which are in contact with the conductive balloon material 120, either directly via a conductor or by conduction through a conductive fluid (e.g., saline) in the balloon, for example.

FIG. 9A shows a balloon 102 which is fabricated to include a multiplicity of discrete fluid conductive regions 120 spaced apart longitudinally and circumferentially to define a generally spiral shape along a surface of the balloon body 103. FIG. 9B illustrates a balloon 102 which is fabricated to include a continuous region 120 that defines a ribbon electrode having a generally spiral shape along a surface of the balloon body 103. FIG. 9C shows a balloon 102 which is fabricated to include a multiplicity of discrete fluid conductive regions 120 spaced apart circumferentially to define a generally circumferential band or annular shape along a surface of the balloon body 103. FIG. 9D shows a balloon 102 which is fabricated to include a continuous region 120 that defines a ribbon electrode having a generally circumferential band or annular shape along a surface of the balloon body 103. It is noted that the fluid conductive region patterns shown in FIGS. 9A-9D can be replicated at one or more longitudinally spaced sections of the balloon body 103.

FIG. 10 illustrates a catheter 200 which is fabricated to include a conductive hydrophilic material in the construction of the balloon body 203 in accordance with various embodiments. As shown in FIG. 10, a relatively short balloon 202 can be made of a conductive polymer. The balloon body 202 may, for example, be formed of a single layer of a conductive hydrophilic polymer. Although not specifically shown in FIG. 10, the lumen arrangement 205 of the shaft 204 may include a guide lumen coupled to an inlet manifold 207 of the balloon 202 and dimensioned to receive a guide wire.

A central or circumferential section 212 of the balloon 202 preferably has a thinner wall than the waist or conical sections 213 a, 213 b. A single electrode is shown situated inside the balloon 202, and RF energy passes through the electrolytic fluid in the balloon 202 and through the conductive polymer central portion 212 of the balloon 202 to ablate a circumferential band of tissue around the renal artery 12. Cooling fluid is used to reduce injury to the renal artery wall, such as a cooled electrolytic fluid.

The balloon 202 is configured to be pressurized to a pressure sufficient to facilitate perfusion of the conductive fluid preferentially through the circumferential section 212 relative to the proximal and distal conical sections 213 a, 213 b. Because the central or circumferential section 212 of the balloon 202 can have a thinner wall than the waist or conical sections 213 a, 213 b, RF energy can be conducted to the artery wall 12 primarily through the circumferential section 212, with little loss from other parts of the balloon (e.g., conical sections 213 a, 213 b). In addition, if the conductive polymer used to construct the balloon 202 has higher electrical resistance than the adjacent tissues, the current density will be relatively uniform around the circumferential section 212.

In the representative embodiment shown in FIG. 10, the balloon body 203 is preferably constructed using a conductive thermoplastic polyurethane, such as the aforementioned Tecophilic™ or Tecogel™ polyurethanes. In the embodiment shown in FIG. 10, all or a substantial part of the balloon body 203 is formed from conductive thermoplastic polyurethane. The thickness of the balloon body wall is varied to define thin and thick walled sections 212, and 213 a, 213 b. The thin walled section or sections 212 serve as RF electrode(s) relative to the thick walled sections 213 a, 213 b. An electrical conductor 210 is shown extending along the shaft 204 and into the balloon body 203. An electrode 215 is situated on the distal end of the conductor 210 and within the balloon body 203. In other embodiments, such as the one shown in FIG. 11, the conductor 210 can extend within or along the thick walled section 213 a.

The catheter 200 shown in FIG. 10 includes a flexible shaft 204 having a proximal end, a distal end, a length, and a lumen arrangement 205 (see, e.g., selected components of lumen arrangement 105 of FIG. 5A) extending between the proximal and distal ends. The length of the shaft 204 is sufficient to access a treatment location of the body, such as a patient's renal artery, relative to a percutaneous location. The catheter 200 includes a balloon 202 provided at the distal end of the shaft 204 and fluidly coupled to the lumen arrangement 205. The distal end of the shaft 204 and the balloon 202 are dimensioned for deployment within the treatment location of the body, such as a patient's renal artery 12.

According to various embodiments, the balloon body 203 is formed of a layer of a hydrophilic polymer that becomes electrically conductive in response to absorption of a conductive liquid. The balloon body 203 preferably includes a proximal conical section 213 a, a distal conical section 213 b, and a circumferential section 212 defined between the proximal and distal conical sections 213 a, 213 b. The circumferential section 212 is configured to contact a circumferential portion of an inner wall of the renal artery 12. The circumferential section 212 has a thickness less than that of the proximal and distal conical sections 213 a, 213 b sufficient to facilitate preferential perfusion of conductive liquid through the circumferential section 212 relative to the proximal and distal conical sections 213 a, 213 b.

The representative embodiment shown in FIG. 10 further includes an inlet manifold 207 coupled to the lumen arrangement 205 through which the electrically conductive liquid can pass into the balloon body 203. An electrical conductor 210 is shown extending at least partially along the shaft 204 and terminating proximate or within the balloon body 203. The electrical conductor 210 is coupled to an electrode 215 positioned within the balloon body 203 and configured to conduct RF energy received from an external energy source (not shown) to at least the circumferential section 212 of the balloon body 203 sufficient to ablate perivascular renal nerves via the circumferential section 212.

A cooling arrangement is provided for at least one of receiving a thermal transfer fluid from the lumen arrangement 205 and facilitating perfusion of blood passing through the renal artery to cool the balloon body 203 during ablation of the perivascular renal nerves. The cooling arrangement may be configured in a manner previously described. In some embodiments, as shown in FIG. 10 for example, a cooled bio-compatible electrolytic fluid, such as saline, can be delivered to the balloon 202 via the lumen arrangement 205, passing through the balloon 203 and exiting at a distal end of the balloon 203. In this configuration, the cooled bio-compatible electrolytic fluid exits into the blood flowing through the renal artery 12. The distal end of the balloon 203 may include a pressure regulated valve which regulates the flow of electrolytic fluid exiting the balloon 203 based on balloon pressure. Proper selection of the pressure regulated valve provides for the development of desired pressure levels within the balloon 202 and a desired volumetric flow rate of bio-compatible electrolytic fluid through the balloon 203.

With reference now to FIG. 11, there is shown a portion of the balloon 203 depicted in FIG. 10. In FIG. 11, the circumferential section 212 is shown to have a thickness, t₁, and the proximal and distal conical sections 213 a, 213 b are shown to have a thickness, t₂. The thickness, t₁, of the circumferential section 212 is less than the thickness, t₂, of the proximal and distal conical sections 213 a, 213 b. The relative thicknesses t₁ and t₂ are selected to facilitate preferential absorption of an electrolytic fluid supplied to the balloon 202 and perfusion of this fluid through the circumferential section 212 relative to the proximal and distal conical sections 213 a, 213 b.

The relative thicknesses t₁ and t₂ of the thin and thick walled sections 212 and 213 a, 213 b can be selected based on a number of factors, including the permeation rate of the fluid through the particular conductive polymer used in the construction of the balloon 202, the working pressures of the balloon 202 (e.g., the expected pressure gradient across the balloon wall 202 during ablation), the surface area of the thin and thick walled sections 212 and 213 a, 213 b, the working temperatures of the balloon 202 as it is heated during ablation, and the fraction of Ohmic heat that is deposited in the balloon wall versus adjacent tissue during ablation, among others.

The length of the circumferential section 212 is preferably less than a length of the proximal and distal conical sections 213 a, 213 b. For example, the length of the circumferential section 212 can be less than about half a length of the proximal and distal conical sections 213 a, 213 b. In some embodiments, the circumferential section 121 can have a length less than 1 mm. In other embodiments, the circumferential section 121 can have a length less than 2 mm. The circumferential section 121 can have a length less than 3 mm in further embodiments. Still in other embodiments, the circumferential section 121 can have a length less than 10 mm.

The balloon 203 depicted in FIG. 11 differs from that shown in FIG. 10 in the terms of the conductor and electrode arrangements. In FIG. 11, the conductor 210 is situated within the wall of the proximal thick walled section 213 a. A distal end of the conductor 210 electrically connects to an electrode element 217. The electrode element 217 can be situated within the wall of the thin walled section 212, or on the interior or exterior surface of the thin walled section 212.

The electrode element 217 may be a continuous metalized layer that extends circumferentially around the thin walled section 212 of the balloon 202. In other configurations, a multiplicity of conductors 210 may be connected to a multiplicity of discrete metalized regions distributed around the thin walled section 212 of the balloon 202 to define spot electrodes. The discrete metalized regions can be individually controlled. In some configurations, a multiplicity of discrete metalized regions can be distributed around the thin walled section 212 of the balloon 202 and connected to a common conductor 210. In this case, the thickness, t₁, of the fluid conductive regions is chosen so that the electrical resistance of the fluid conductive regions is greater than the resistance of adjacent body tissues, providing uniform current density through the multiplicity of fluid conductive regions.

FIG. 12 shows an alternative embodiment of the electrode configuration at the circumferential section 212 of the balloon 202 shown in FIG. 11. The configuration shown in FIG. 12 includes a conductive hydrophilic polymer region 220 disposed on an exterior surface of a non-conductive polymer balloon 203. The conductive hydrophilic polymer region 220 defines an RF electrode 217 in response to absorption of the conductive liquid and is electrically coupled to a conductor 210 situated within the wall of the balloon body 203. A number of holes or slits 201 are provided in the balloon wall adjacent the conductive hydrophilic polymer region 220. The holes or slits 201 provide for the communication of an electrolytic fluid from the balloon interior to the conductive hydrophilic polymer region 220.

FIG. 13 shows another embodiment of the electrode configuration at the circumferential section 212 of the balloon 202 shown in FIG. 11. The configuration shown in FIG. 13 includes a conductive pad or pad elements 222 disposed on an exterior surface of a surface of the non-conductive polymer balloon 203. The conductive pad or pad elements 222 may be formed using one or more metalized layers. A conductive hydrophilic polymer region 220 is disposed over the conductive pad or pad elements 222, such that the conductive pad or pad elements 222 are completely covered by the conductive hydrophilic polymer material of region 220. The conductive pad or pad elements 222 and conductive hydrophilic polymer region 220 define an RF electrode 217 in response to absorption of the conductive liquid by the hydrophilic polymer material.

In the embodiment shown in FIG. 13, an electrical conductor 210 is spaced apart from the conductive hydrophilic polymer region 220. Preferably the electrical conductor 210 extends from the catheter shaft and into the balloon interior. Alternatively, the electrical conductor 210 can be situated within the wall of the balloon. A number of holes or slits 201 are provided in the balloon wall and the conductive pad or pad elements 222 to define channels between the balloon interior and the conductive hydrophilic polymer region 220. RF energy is conducted from the conductor 210 to the conductive hydrophilic polymer region 220 via the electrolytic fluid supplied to the balloon interior and absorbed by the conductive hydrophilic polymer region 220.

In accordance with one fabrication method, a nonconductive balloon is formed, and a metalized layer accommodating electrode patches or lines and conductive traces to connect to one or more supply conductors is applied. A pattern of holes or slits is cut into the balloon at the electrode locations, and a fluid conductive polymer is applied creating a sandwich with the metalized layer inside, with only the fluid conductive polymer layer at the electrode locations. Additional layers can be applied for support or other properties if desired.

According to another embodiment, fluid conductive balloon material patches can be applied to the outside of a standard nonconductive balloon, with insulated electrically conductive paths leading to the patches. Metalized portions under the conductive patches can supply RF energy to the fluid conductive patches. For example, a balloon can include a standard nonconductive material that has holes in it, with a layer of fluid conductive balloon material inside or outside to cover the holes. Additional reinforcing fibers or mesh can be incorporated as well.

Small holes can be cut through the balloon to provide irrigating cooling to further protect the renal artery from thermal injury during RF ablation. These small holes can be remote from any metalized portions to reduce the passage of RF energy through the irrigation holes.

According to other embodiments, combinations of one or more of fluid conductive balloon material portions covering holes in nonconductive balloon material, conductive balloon material patches applied to the outside of nonconductive balloon material, and metalized portions can be used to provide a desired spatial pattern of RF electrodes. For example, saline in the balloon can conduct energy to the fluid conductive balloon material which conducts through the wall to apply RF energy to select locations in the renal artery, and conductive balloon material patches or metalized portions on the exterior of the balloon can apply RF energy to other locations in the renal artery, and so forth.

Thermocouples or other sensors can be incorporated. Unipolar or bipolar arrangements can be utilized. Over-the-wire, fixed-wire, or no-wire systems can be used, with guiding sheaths or catheters as needed to properly position the catheter.

It is to be understood that even though numerous characteristics of various embodiments have been set forth in the foregoing description, together with details of the structure and function of various embodiments, this detailed description is illustrative only, and changes may be made in detail, especially in matters of structure and arrangements of parts illustrated by the various embodiments to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed. 

What is claimed is:
 1. An apparatus, comprising: a catheter comprising a flexible shaft having a proximal end, a distal end, a length, and a lumen arrangement extending between the proximal and distal ends, the length of the shaft sufficient to access a renal artery of a patient relative to a percutaneous access location; a balloon provided at the distal end of the shaft and fluidly coupled to the lumen arrangement, the distal end of the shaft and the balloon dimensioned for deployment within the renal artery, the balloon comprising: a balloon body formed of a hydrophilic polymer that becomes electrically conductive in response to absorption of a conductive liquid, the balloon body comprising a proximal conical section, a distal conical section, and a circumferential section defined between the proximal and distal conical sections and configured to contact a circumferential portion of an inner wall of the renal artery, the circumferential section having a wall thickness less than that of the proximal and distal conical sections sufficient to facilitate preferential perfusion of the conductive liquid through the circumferential section relative to the proximal and distal conical sections; and an inlet manifold coupled to the lumen arrangement through which the electrically conductive liquid can pass into the balloon body; an electrical conductor extending at least partially along the shaft and terminating proximate or within the balloon body, the electrical conductor coupled to an electrode positioned within the balloon body and configured to conduct electrical energy received from an external energy source to at least the circumferential section of the balloon body sufficient to ablate perivascular renal nerve tissue proximate the circumferential section; and a cooling arrangement configured for at least one of receiving a thermal transfer fluid from the lumen arrangement and facilitating perfusion of blood passing through the renal artery to cool the balloon body during ablation of the perivascular renal nerve tissue.
 2. The apparatus of claim 1, wherein the hydrophilic polymer comprises a fluid conductive thermoplastic polyurethane.
 3. The apparatus of claim 1, wherein the balloon is configured to be pressurized to a pressure sufficient to facilitate perfusion of the conductive liquid preferentially through the circumferential section relative to the proximal and distal conical sections.
 4. The apparatus of claim 1, wherein a length of the circumferential section is less than about half a length of the proximal and distal conical sections.
 5. The apparatus of claim 1, wherein the electrical conductor terminates within the balloon body and is coupled to an electrode positioned within the balloon body, the electrode positioned in a space-apart relationship relative to the circumferential section.
 6. The apparatus of claim 1, wherein the electrical conductor extends along at least the proximal conical section and connects with the circumferential section.
 7. The apparatus of claim 1, wherein the balloon body comprises a metalized layer extending along at least the proximal conical section and connecting with the circumferential section.
 8. The apparatus of claim 1, wherein the balloon body is formed of a single layer of the hydrophilic polymer.
 9. The apparatus of claim 1, wherein the lumen arrangement of the shaft comprises a guide lumen coupled to the inlet manifold of the balloon and dimensioned to receive a guide wire.
 10. A method, comprising: passing an electrically conductive liquid into a balloon positioned within a renal artery of a patient, the balloon having a balloon body comprising a first material and one or more fluid conductive regions provided on the balloon body and comprising a second material different from the first material, the second material comprising a hydrophilic polymer that becomes electrically conductive in response to absorption of the conductive liquid, the one or more fluid conductive regions facilitating perfusion of the conductive liquid through the balloon body to an inner wall of the renal artery; communicating electrical energy to the one or more fluid conductive regions sufficient to ablate perivascular renal nerve tissue proximate the renal artery; and at least one of receiving a thermal transfer fluid and facilitating perfusion of blood passing through the renal artery to provide cooling to the balloon body during ablation of the perivascular renal nerve tissue. 